GENETIC-VARIATION IN LOCOMOTOR-ACTIVITY RHYTHM AMONG POPULATIONS OF LEPTOPILINA-HETEROTOMA (HYMENOPTERA, EUCOILIDAE), A LARVAL PARASITOID OF DROSOPHILA SPECIES

The locomotor activity rhythm of Leptopilina heterotoma, a parasitoid insect of Drosophila larvae, was investigated under laboratory conditi ons. Under LD 12:12, the locomotor activity of females shows a clear r hythm which persists under continuous darkness (circadian rhythm). How ever, comparative study of five populations indicates that both the ra te of activity and the profile of the rhythm Vary according to the ori gin of females. The Mediterranean populations (Tunisia and Antibes) sh ow two peaks of activity, at the beginning and at the end of the photo phase, whereas more northern populations (Lyon and the Netherlands) ar e mostly active during the afternoon. Females originating from the are a of Lyon have a very low level of activity. Reciprocal crosses (F-1 h ybrids and backcrosses) between the French and the Tunisian strains de monstrated the genetic basis of these variations and the biparental in heritance of the trait. This genetic variability is interpreted as a c onsequence of selective pressures and suggests a local adaptation of n atural populations in host foraging behavior. The selective factors wh ich could act on the daily organization of parasitoid behaviors are di scussed.